^{Zimbrick, J. D.} Radiation Chemistry and the Radiation Research Society: A History from the Beginning. Radiat. Res. 158, 127–140 (2002).

Radiation chemistry studies began in the early 20th century with observations involving the decomposition of various materials by X rays and radium. Hugo Fricke recognized that the chemical effects of radiation should be studied to help understand the response of living systems to radiation, and in 1928 he established a laboratory to conduct such studies. Early radiation chemists were intimately involved in the founding of the Radiation Research Society and contributed substantially to its interdisciplinary culture. In this historical review, the highlights of research in radiation chemistry leading up to the founding of the Radiation Research Society in 1952 are discussed. The status of the field is established at that point, and a sampling of the major accomplishments from then until the present is presented, with emphasis on those scientists who have contributed substantially to the life and culture of the Radiation Research Society.

Fowler, J. F. Repair between Dose Fractions: A Simpler Method of Analyzing and Reporting Apparently Biexponential Repair. Radiat. Res. 158, 141–151 (2002).

Increasing numbers of animal experiments in situ are reporting that repair of sublethal radiation damage in vivo slows down with time, usually described as two components of (monoexponential) repair. For repair of DNA strand breaks, plotting the reciprocal of proportion unrepaired as a function of time yielded straight lines. Two processes have been suggested as causing this: (1) a second-order process (bimolecular) instead of first-order (exponential) and (2) a skewed distribution of monoexponential rates. The present paper investigates whether such plots of hyperbolic or reciprocal repair are relevant for laboratory animal tissue results. Published repair data were reanalyzed from laboratory animal experiments that employed split doses or two fractions per day. Graphs are presented of the reciprocal proportion of damage remaining as a function of the interval between the two doses. If the reciprocal model applies, the graphs would be straight lines. Different animal data showed no inconsistency with straight reciprocal plots. These reciprocal plots describe well with one parameter τ, the first half-time, repair curves previously thought to be “biexponential”, and to require three parameters. Straight reciprocal plots mean that in a constant time interval τ the unrepaired damage falls from 1 to ½, then from ½ to ⅓, then ⅓ to ¼, etc. A much larger proportion of damage would therefore remain unrepaired at several half-times than is estimated by current mono- or biexponential models. The practical implications for clinical radiotherapy are important.

Yu, H., Su, M-Y., Wang, Z. and Nalcioglu O., A Longitudinal Study of Radiation-Induced Changes in Tumor Vasculature by Contrast-Enhanced Magnetic Resonance Imaging. Radiat. Res. 158, 152–158 (2002).

Dynamic contrast-enhanced MRI with two different-sized contrast agents, Gd-DTPA and Gadomer-17, was used to study the effects of radiation on the pharmacokinetics of the paramagnetic enhancement of water relaxation in the rat R3230 AC adenocarcinoma tumor model. The kinetics of enhancement was analyzed by a two-compartment pharmacokinetic model to derive parameters related to vascular volume (V_b) and permeability (K₂). Rats implanted with tumors were divided into two groups; one received 5 Gy and the other received 20 Gy ¹³⁷Cs γ rays. Sequential dynamic contrast-enhanced MRI studies were performed, one before irradiation, one at day 1 after irradiation, and another at day 3 after irradiation, to investigate the effect of the radiation dose and the changes that occurred over time. The analysis was performed on a pixel-by-pixel basis to study the heterogeneity within the tumor. The pixel distribution profiles of V_b and K₂ from each tumor were obtained to assess the regional radiation-induced effects on vascular volume and permeability. No significant change in vascular volume was detected with either Gd-DTPA or Gadomer-17 after irradiation of the tumor; however, a small dependence of K₂ on the radiation dose was observed. After low-dose (5 Gy) irradiation, the mean value of K₂ decreased by 46% at day 1 compared to the baseline, presumably due to cell swelling, and decreased further by 67% from the baseline on day 3. When the dose was increased to 20 Gy, the mean value of K₂ measured with Gadomer-17 did not show any significant changes at either day 1 or day 3 after irradiation. The value of K₂ measured with Gd-DTPA did not show any significant changes after either the low or the high radiation dose.

Olive, P. L., Banáth, J. P. and Durand, R. E. The Range of Oxygenation in SiHa Tumor Xenografts. Radiat. Res. 158, 159–166 (2002).

Tumor cells at very low oxygen tensions are known to be about three times more resistant to killing by ionizing radiation. Since cells at intermediate oxygen tensions (defined here as greater than 0.1% and less than 2% O₂) show partial radioresistance, they should be a consideration in tumor treatment. In an effort to estimate the extent and range of oxygenation in SiHa human cervical carcinoma xenografts, patterns of cell killing and DNA damage by radiation and two bioreductive drugs, PD-144872 and RSU-1069, were compared to those seen in SiHa cells grown as spheroids. These drugs produce DNA interstrand crosslinks that are largely responsible for cell killing, and the degree of crosslinking increases as the oxygenation is reduced. About 60% of the cells in SiHa xenografts exhibited drug-induced crosslinks, but only about 35% showed extensive crosslinking indicative of hypoxia below 0.1% oxygen. Patterns of toxicity and DNA damage in xenografts were comparable to those of spheroids equilibrated with about 2% oxygen, indicating that most cells in the xenografts exhibit some radioresistance due to lack of oxygen. Similarly, pimonidazole binding indicated that about 60% of the cells in SiHa xenografts were either intermediate in oxygenation or hypoxic, but only about half of those were consistent with extreme oxygen depletion. The apparent size of the population of “intermediately hypoxic” cells has implications for the use of ionizing radiation, hypoxic cell cytotoxins, and other antitumor agents whose cytotoxicity is dependent on cellular oxygen content.

Urano, M., Chen, Y., Humm, J., Koutcher, J., Zanzonico, P. and Ling, C. Measurements of Tumor Tissue Oxygen Tension Using a Time-Resolved Luminescence-Based Optical OxyLite Probe: Comparison with a Paired Survival Assay. Radiat. Res. 158, 167–173 (2002).

Recently, a system that measures tissue oxygen tension using time-resolved luminescence-based optical sensors has become available commercially (Oxford Optronix, Oxford, England). Two experiments were conducted using this system. First, the oxygen tension distribution was measured in two tumor lines: a spontaneous mouse fibrosarcoma, FSa-II, and a human squamous cell carcinoma xenograft, FaDu. The area in which the pO₂ was equal to or lower than 2.5 mmHg was defined as the hypoxic lesion, and the hypoxic cell fraction was taken as the fraction of these measurements in a tumor. The measured hypoxic cell fractions were compared with those determined by the paired cell survival assay for tumors of various sizes. Second, the tumor tissue pO₂ was measured continuously after administration of two different anesthetics to evaluate the effect of these drugs on tissue pO₂. Results indicated a good agreement between the hypoxic cell fractions measured by this system and those determined by the paired cell survival curve assay for tumors smaller than ∼500 mm³. For tumors larger than ∼500 mm³, the hypoxic cell fractions measured by the oxygen probe system were higher than those measured by the paired cell survival assay. This may suggest that the hypoxic cell fraction measured by the oxygen probes included both hypoxic and necrotic areas in large tumors where necrotic lesions occupied a significant portion of the tumor. Continuous measurements of pO₂ after anesthesia (Nembutal, or ketamine plus xylazine) showed a consistent rise in the pO₂ during the first 20–30 min of measurement. Subsequently, the pO₂ values became constant or continued to rise slowly. For comparison, the tumor cell survivals were assayed after a dose of 20 Gy given in air at 5, 20 and 60 min after anesthesia. The result showed a decrease in cell survival only in tumors irradiated 20 min after an injection of Nembutal.

Peretz, S., Kim, C., Rockwell, S., Baserga, R. and Glazer, P. M. IGF1 Receptor Expression Protects against Microenvironmental Stress Found in the Solid Tumor. Radiat. Res. 158, 174–180 (2002).

The insulin-like growth factor 1 receptor (IGF1R) is a tyrosine kinase, transmembrane receptor expressed in most body tissues and required for normal growth of cells. In cell culture, overexpression of the receptor has been shown to promote transformation and enhance cell survival in response to selected cytotoxic agents. As tumors develop, abnormalities in vascularization lead to a heterogeneous environment that includes areas of hypoxia, low pH and low glucose. Here we report that the overexpression of the IGF1R promotes increased survival in cells exposed to hypoxia, low pH and low glucose. Furthermore, cells lacking the receptor due to targeted disruption of the IGF1R gene do not survive as well as normal cells in such conditions. In addition, we find that cells can activate the IGF1R gene promoter in response to these conditions, and immunoblot analyses show increased receptor protein levels in cell exposed to hypoxia. Our results suggest a pathway of cancer cell adaptation to the tumor microenvironment in which conditions of the environment may induce expression of IGF1R, and this subsequent overexpression of the receptor may increase cell survival in such conditions.

Broome, E. J., Brown, D. L. and Mitchel, R. E. J. Dose Responses for Adaption to Low Doses of ⁶⁰Co γ Rays and ³H β Particles in Normal Human Fibroblasts. Radiat. Res. 158, 181–186 (2002).

The dose response for adaption to radiation at low doses was compared in normal human fibroblasts (AG1522) exposed to either ⁶⁰Co γ rays or ³H β particles. Cells were grown in culture to confluence and exposed at either 37°C or 0°C to ³H β-particle or ⁶⁰Co γ-ray adapting doses ranging from 0.1 mGy to 500 mGy. These cells, and unexposed control cells, were allowed to adapt during a fixed 3-h, 37°C incubation prior to a 4-Gy challenge dose of ⁶⁰Co γ rays. Adaption was assessed by measuring micronucleus frequency in cytokinesis-blocked, binucleate cells. No adaption was detected in cells exposed to ⁶⁰Co γ radiation at 37°C after a dose of 0.1 mGy given at a low dose rate or to 500 mGy given at a high dose rate. However, low-dose-rate exposure (1–3 mGy/min) to any dose between 1 and 500 mGy from either radiation, delivered at either temperature, caused cells to adapt and reduced the micronucleus frequency that resulted from the subsequent 4-Gy exposure. Within this dose range, the magnitude of the reduction was the same, regardless of the dose or radiation type. These results demonstrate that doses as low as (on average) about one track per cell (1 mGy) produce the same maximum adaptive response as do doses that deposit many tracks per cell, and that the two radiations were not different in this regard. Exposure at a temperature where metabolic processes, including DNA repair, were inactive (0°C) did not alter the result, indicating that the adaptive response is not sensitive to changes in the accumulation of DNA damage within this range. The results also show that the RBE for low doses of tritium β-particle radiation is 1, using adaption as the end point.

Carnes, B. A., Gavrilova, N. and Grahn, D. Pathology Effects at Radiation Doses below those Causing Increased Mortality. Radiat. Res. 158, 187–194 (2002).

Mortality data from experiments conducted at the Argonne National Laboratory (ANL) on the long-term effects of external whole-body irradiation on B6CF₁ mice were used to investigate radiation-induced effects at intermediate doses of ⁶⁰Co γ rays or fission-spectrum neutrons either delivered as a single exposure or protracted over 60 once-weekly exposures. Kaplan-Meier analyses were used to identify the lowest dose in the ANL data (within radiation quality, pattern of exposure, and sex) at which radiation-induced mortality caused by primary tumors could be detected (approximately 1–2 Gy for γ rays and 10–15 cGy for neutrons). Doses at and below these levels were then examined for radiation-induced shifts in the spectrum of pathology detected at death. To do this, specific pathology events were pooled into larger assemblages based on whether they were cancer, cardiovascular disease or non-neoplastic diseases detected within the lungs and pleura, liver and biliary tract, reproductive organs, or urinary tract. Cancer and cardiovascular disease were further subdivided into categories based on whether they caused death, contributed to death, or were simply observed at death. Counts of how often events falling within each of these combined pathology categories occurred within a mouse were then used as predictor variables in logistic regression to determine whether irradiated mice could be distinguished from control mice. Increased pathology burdens were detected in irradiated mice at doses lower than those causing detectable shifts in mortality—22 cGy for γ rays and 2 cGy for neutrons. These findings suggest that (1) models based on mortality data alone may underestimate radiation effects, (2) radiation may have adverse health consequences (i.e. elevated health risks) even when mortality risks are not detected, and (3) radiation-induced pathologies other than cancer do occur, and they involve multiple organ systems.

Tsuchida, R., Yamada, T., Takagi, M., Shimada, A., Ishioka, Katsuki, Y., C., Igarashi, T., Chessa, L., Delia, D., Teraoka, H. and Mizutani, S. Detection of ATM Gene Mutation in Human Glioma Cell Line M059J by a Rapid Frameshift/Stop Codon Assay in Yeast. Radiat. Res. 158, 195–201 (2002).

A yeast-based frameshift/stop codon assay for examining ATM (ataxia telangiectasia mutated) mutations was established. Each of six fragments of a PCR-amplified coding sequence for ATM is inserted in frame by homologous recombination into a yeast URA3 fusion protein gene, and the transformants are assayed for growth in the absence of uracil. The usefulness of this assay was verified in a panel of cell lines derived from individuals with homozygous and heterozygous ATM mutations. The assay was also shown to distinguish between specimens with wild-type alleles and those with truncating mutations: a frameshift mutation or an inserted stop codon. Using this assay M059J cells, which fail to express the catalytic subunit of DNA-dependent protein kinase (PRKDC, also known as DNA-PKcs) and are hypersensitive to ionizing radiation, were found to express two different aberrant ATM transcripts: one characterized by 4776 del 133, which corresponds to the deletion of exon 33, and the other by 4909 ins 116. Subsequent analysis of the intron sequences revealed that 4909 ins 116 is comprised of a nucleotide sequence corresponding to 84013–84128 in intron 33 with a cryptic splice site. Thus the radiosensitive phenotype of M059J cells appears to be due to a defect in PRKDC and a truncating ATM mutation.

Kashiwakura, I., Inanami, O., Murakami, M., Takahashi, T. A., Kuwabara, M. and Takagi, Y. Effects of the Combination of Thrombopoietin with Cytokines on the Survival of X-Irradiated CD34 Megakaryocytic Progenitor Cells from Normal Human Peripheral Blood. Radiat. Res. 158, 202–209 (2002).

Combinations of thrombopoietin and cytokines that act on megakaryocyte development (stem cell factor, IL3, IL6, IL11, flt3 ligand (now known as FLT3LG), erythropoietin, GM-CSF and G-CSF were evaluated for their ability to enhance clonal growth in vitro of X-irradiated CD34 megakaryocytic progenitor cells (CFU-megakaryocytes) purified from normal human peripheral blood. These data were compared with corresponding results described previously for CD34 CFU-megakaryocytes from human placental/umbilical cord blood (I. Kashiwakura, Radiat. Res. 153, 144–152, 2000). All cytokines, except IL3, promoted thrombopoietin-induced colony formation, but they resulted in exponential radiation survival curves. No significant differences in the D₀ (46–61 cGy) and extrapolation number n (1.00–1.04) were observed between thrombopoietin alone and in combination with these cytokines. IL3 did not promote colony formation, but marked shoulders were observed on the survival curves (D₀ = 91 cGy, n = 2.83). Flow cytometric analysis of cells harvested from cultures of X-irradiated cells stimulated with thrombopoietin plus IL3 showed no significant differences in the expression of surface antigens and DNA ploidy distribution of megakaryocytes from the control. These findings suggest that IL3 plays a key role in promoting the survival of X-irradiated CD34 CFU-megakaryocytes from peripheral blood as well as those from cord blood, though the former are more radiosensitive.

Rugo, R. E., Secretan, M. B. and Schiestl, R. H. X Radiation Causes a Persistent Induction of Reactive Oxygen Species and a Delayed Reinduction of TP53 in Normal Human Diploid Fibroblasts. Radiat. Res. 158, 210–219 (2002).

Multiple genetic changes are required for the development of a malignant cell. The frequency of such changes in cancer cells is higher than can be explained through random mutation, and it was proposed that a subpopulation of cells develop a persistent mutator phenotype. Evidence for such a phenotype has been observed in mammalian cells after treatment with ionizing radiation. The mechanism that promotes this effect has not been defined, but proposed explanations include increased levels of reactive oxygen species (ROS) in irradiated cells and their progeny. The tumor suppressor TP53 is of prime importance in coordinating the cellular response to damage, and it has been suggested to have a role in regulating the cellular redox state. We investigated the persistence of induced levels of ROS in normal diploid human cells for 1 month after X-ray exposure and the role of TP53 in this oxidant response. X radiation induced an oxidant response that persisted for 2 weeks after exposure in cells with normal TP53 function. ROS levels in cells with abrogated TP53 function were decreased in magnitude and duration. X radiation caused a primary transient induction of TP53 followed by a reinduction of TP53 5 days after irradiation. This reinduction persisted for at least 2 days and coincided with the largest induction of apoptosis. The persistently elevated levels of ROS and delayed reinduction of TP53 reported here are further evidence of the delayed effects of ionizing radiation and add to the growing number of such observations.

Preston, D. L., Mattsson, A., Holmberg, E., Shore, R., Hildreth, N. G. and Boice, J. D., Jr. Radiation Effects on Breast Cancer Risk: A Pooled Analysis of Eight Cohorts. Radiat. Res. 158, 220–235 (2002).

Breast cancer incidence rates after radiation exposure in eight large cohorts are described and compared. The nature of the exposures varies appreciably, ranging from a single or a small number of high-dose-rate exposures (Japanese atomic bomb survivors, U.S. acute post-partum mastitis patients, Swedish benign breast disease patients, and U.S. infants with thymic enlargement) to highly fractionated high-dose-rate exposures (two U.S. tuberculosis cohorts) and protracted low-dose-rate exposure (two Swedish skin hemangioma cohorts). There were 1,502 breast cancers among 77,527 women (about 35,000 of whom were exposed) with 1.8 million woman-years of follow-up. The excess risk depends linearly on dose with a downturn at high doses. No simple unified summary model adequately describes the excess risks in all groups. Excess risks for the thymus, tuberculosis, and atomic bomb survivor cohorts have similar temporal patterns, depending on attained age for relative risk models and on both attained age and age at exposure for excess rate models. Excess rates were similar in these cohorts, whereas, related in part to the low breast cancer background rates for Japanese women, the excess relative risk per unit dose in the bomb survivors was four times that in the tuberculosis or thymus cohorts. Excess rates were higher for the mastitis and benign breast disease cohorts. The hemangioma cohorts showed lower excess risks suggesting ameliorating dose-rate effects for protracted low-dose-rate exposures. For comparable ages at exposure (∼0.5 years), the excess risk in the hemangioma cohorts was about one-seventh that in the thymus cohort, whose members received acute high-dose-rate exposures. The results support the linearity of the radiation dose response for breast cancer, highlight the importance of age and age at exposure on the risks, and suggest a similarity in risks for acute and fractionated high-dose-rate exposures with much smaller effects from low-dose-rate protracted exposures. There is also a suggestion that women with some benign breast conditions may be at elevated risk of radiation-associated breast cancer.

Yamada, M., Sasaki, H., Kasagi, F., Akahoshi, M., Mimori, Y., Kodama, K. and Fujiwara, S. Study of Cognitive Function among the Adult Health Study (AHS) Population in Hiroshima and Nagasaki. Radiat. Res. 158, 236–240 (2002).

Although neuropsychological dysfunction is found among A-bomb survivors exposed in utero as it is among patients who receive central nervous system radiotherapy, neuropsychological examinations have not been conducted on the survivors. Its prevalence may be increased as a result of the increased rate of strokes reported among those exposed to a high radiation dose. In this study, we examined the effects of radiation exposure on cognitive function among adult survivors in the Adult Health Study (AHS). The study subjects were men and women born prior to September 1932 who had undergone biennial examinations during the period 1992–1996 in Hiroshima or 1993–1998 in Nagasaki. We evaluated cognitive performance for 3,113 subjects with the Cognitive Abilities Screening Instrument (CASI), and we examined the relationship between cognitive performance and potentially related factors (sex, age, city where the subjects were exposed, years of education, and radiation dose). In contrast to exposure to radiotherapy, exposure to atomic bomb radiation had no apparent effect on cognitive function. Factors that did affect cognitive function were age, sex, city and years of education. Further investigation, including examination of other neurological functions, is required before a final conclusion regarding radiation-induced neurological dysfunction can be reached.

Koizumi, H., Sasaki, T. and Ichikawa, T. Radiation-Induced Chain Reactions in Alcohol Solutions of Diphenyliodonium Salts: A High-Sensitivity Chemical Dosimeter. Radiat. Res. 158, 241–246 (2002).

Chain reactions in γ-irradiated 2-propanol solutions of diphenyliodonium salts have been studied. Protonic acids were generated in the irradiated solutions with high yields, whereas acid formation as a result of thermal reactions was negligible. The solution can be used as a high-sensitivity chemical dosimeter. The G value of acidic protons increases with increasing concentration of diphenyliodonium salt at the lower concentrations because the reaction rate of a propagation reaction increases. However, the chain is limited by a termination reaction between phenyl radical and the iodonium salt: The G value shows a maximum value of 610 μmol J⁻¹ at the concentration of 0.08 mol dm⁻³ and decreases at higher salt concentrations.

Cedervall, B. E. and McMillan, T. J. The Fraction of DNA Released on Pulsed-Field Gel Electrophoresis Gels may Differ Significantly between Genomes at Low Levels of Double-Strand Breaks. Radiat. Res. 158, 247–249 (2002).

A common way to use pulsed-field gel electrophoresis (PFGE) for measuring the induction and repair of DNA double-strand breaks (DSBs) in mammalian cells is by using the fraction of total DNA released, FR, from the plug. We have analyzed the general relationship between initial chromosome sizes and FR. It is shown that, because of the difference in initial chromosomal size, the discrepancy in FR values between human and rodent cells may become significant at doses of radiation producing ∼5 DSBs/100 Mbp or less.